I'm surprised this hasn't had more attention. I was going to make a similar post. I had a thought of importing one to the UK and then having the engine swapped over into my E90 BMW 335D Chasis. A lot of money I know, but the end result would be AMAZING!!!!!!

The engine wasn't designed with the DPF in mind. BMW stated they specifically weren't bringing this car over because there was no room to include the additional emissions equipment necessary for the US.

The exhaust treatment system includes a diesel particulate filter and oxidation catalytic converter, which is located close to the engine in the same casing. More efficient exhaust cooling, meanwhile, minimises the formation of nitrogen oxides. And standard-fitted BMW BluePerformance technology, which includes a NOX storage catalytic converter, helps the new diesel engine powering the BMW M550d xDrive to meet the EU6 exhaust standard not due to come into force until 2014.